The present invention relates to the art of plasma arc torches and, more particularly, to improvements in connection with the flow of gas therethrough for cooling and operating the torch.
It is of course well known that a plasma arc torch comprises an electrode and a nozzle in which a nose end of the electrode is supported for the end of the nose of the electrode to face an end wall of the nozzle which has a plasma outlet opening therethrough. The electrode and nozzle may be relatively displaceable between a position in which the electrode contacts the end wall of the nozzle and a position in which the electrode is spaced an operating distance from the end wall, whereby a pilot arc can be created as the electrode moves away from the end wall to its operating position. Alternatively, the electrode and nozzle can be fixed relative to one another, whereby the torch is started by the use of high frequency or other known starting procedures. In any event, the end wall of the nozzle and the end face of the electrode provide a gas chamber into which a plasma or arc gas is supplied and from which a plasma jet is emitted through the outlet opening when an arc current is flowed between the electrode and nozzle. Upon starting the torch, the latter operates in a non-transferred pilot arc mode and, by moving the nozzle into proximity with the work piece, the arc is transferred thereto and the torch then operates in the arc-transferred mode. Such torches are of course well known for use in connection with heating, welding, cutting, melting, annealing, and the like.
It is also known in connection with plasma arc torches of the foregoing character to impart a swirling motion to the plasma gas upstream of the gas chamber for cooling purposes and in an effort to keep the emitted plasma jet focused on line with the axis of the electrode. Such swirling is helpful in producing a good quality plasma arc, improving cutting speed and in promoting economy and efficiency with-respect to the work performed and operation of a torch. It is also known to direct swirling gas inwardly across the end surface of the electrode in a fixed electrode to nozzle arrangement for removing products of erosion from the nozzle to increase the life thereof. Other efforts with respect to controlling gas flow have included the swirling of gas about the plasma jet as it exits the outlet opening through the nozzle for stabilizing the plasma jet against lateral wandering, and reducing the amount of swirling and the velocity of the plasma gas entering the gas chamber and prior to the exiting of the plasma jet therefrom so as to achieve a smooth flow of the plasma gas and to maintain stability of the arc jet in the torch. Swirling of the gas prior to entrance thereof into the gas chamber between the electrode and the plasma jet outlet has included the radially inwardly directing of swirling gas about the nose end of the electrode for stabilizing the plasma jet against lateral wandering.
While efforts such as those mentioned above have been operable at least to some extent to control the direction of the plasma jet and to provide a shield thereabout, it remains that the swirling of the gas degenerates between the point of its creation and the plasma jet outlet whereby the desired constricting of the jet to follow a straight line between the nozzle and a workpiece is not fully achieved. Furthermore, the arrangements heretofore provided in an effort to obtain the desired control of the plasma jet as well as the flow of a shield gas thereabout have been structurally complex and thus undesirably expensive to manufacture and maintain. With regard to degeneration of the swirling motion, once the gas exits the passageway or passageways by which the swirling motion is imparted thereto the gas travels to and through the gas chamber to the plasma jet outlet opening along interior surfaces of the nozzle which are smooth and therefore ineffective for maintaining the initial swirling movement. Moreover, the swirling gas most often experiences a pressure drop as it exits the passage or passageways by which it is created and such a pressure drop also contributes to degeneration of the swirling flow pattern.